1. Field of the Invention
This invention relates to altering the temperature, humidity and the presence of physical and biological contaminants of gases used to inflate body cavities prior to and during medical procedures. More specifically, it relates to a compact device for, and method of, heating, humidifying and filtering insufflation gases at a point immediately prior to passage of the gases into the patient.
2. Background Art
From the beginning of laparoscopic surgical procedures some twenty years ago, it has been assumed that the condition of gases used to inflate body cavities were physiologically and pathologically benign. While the importance and use of temperature and moisture conditioning of anesthesia gases has been well known, until recently little attention had been given to the particulate, temperature and/or humidity condition of insufflation gases used to create a pneumoperitoneum.
A commonly used insufflation gas is carbon dioxide which is typically provided as a liquid in compressed gas cylinders. The pressure in these cylinders, when at equilibrium with ambient environment of 20.degree. C., is 57 atmospheres (5740 KPa). The carbon dioxide gas is typically provided to the surgical site at a pressure of 15 mmHg via an adjustable, throttling pressure regulator and flow controller called an insufflator. Many models of insulators are available such as the Storz Model 26012 (Karl Storz Endoscopy-America Inc., Culver City, Calif.). In general, insulators do not filter, control the temperature of or humidify the gas.
When the insufflator provides gas flows of various magnitudes, typically 1 to 10 liters per minute, it must reduce the gas pressure of the gas from the cylinder pressure from about 57 atmosphere to approximately 1 atmosphere. Such a process is called "throttling," which causes the gas to be cooled via a thermodynamic process known as Joule-Thompson cooling (see, for example, Y. A. Cengel and M. A. Boles, "Thermodynamics: An Engineering Approach," McGraw-Hill, (1988)).
With the carbon dioxide as the insufflation gas, Joule-Thompson cooling can reduce the gas temperature as much as 50.degree. to 70.degree. C., depending on gas mass flow rates. The fortuitous, large difference in heat capacities of the insufflator metal hardware (large) and the CO.sub.2 gas stream (small) permits the gas stream to be reheated to approximately operating room ambient temperature (around 20.degree. C.) before the gas enters the patient. In the case of large gas flows, this unplanned and uncontrolled reheating effect could be incomplete and the insufflator gas could leave the insufflator apparatus at temperatures considerably less than. the ambient temperature of approximately 20.degree. C. In any case, insufflator gas cannot reach a temperature higher than this ambient temperature, and hence, the insufflator gas enters the patient at a temperature substantially less (at least 17.degree. C. less) than the patient's physiological core of approximately 37.degree. C. (Ott, D. E., J. Laparoendosc. Surg., 1:127-131 (1991)).
Newly developed insufflators and ancillary devices have recognized this problem and have attempted to correct it by adding heat to the gas stream before it enters the delivery system which directs the gas to the trocars (see, for example, Computerized High Flow Insufflator (Snowden-Pencer, Inc., Tucker, Ga.) and Flow-Therme (Wisap U.S.A., Tomball, Tex.)). This method is thermodynamically unsound because it fails to recognize the thermal-capacity mismatch between the flowing gas stream and the gas delivery system between the insufflator and the trocar incision point at the abdomen, even when the delivery system is only 6 to 10 feet of polymer tubing. In addition, this method overlooks the above heat transfer that occurs between the gas stream and the ambient temperature gas delivery tubing. Because of these thermal conditions, the temperature of any gas preheated at or in the insufflator itself will return to approximately the ambient temperature after flowing as little as four (4) feet after leaving the insufflator.
U.S. Pat. No. 5,006,109 (Douglas et al. ) relocates the temperature sensor to the point of gas administration, but this relocation does not solve this problem, because as has been mentioned above, that point can be, in practice, 6 to 10 feet from any temperature controller. Such an arrangement leads, with the low flow rates typically used in these surgical methods, to "transportation lags" which render stable feedback control difficult to achieve under major, rapid flow rate changes which are typically required by these endoscopic and laparoscopic surgical procedures. Thus, the gas reaches the patient at a temperature much lower than the desirable 36.degree. C.-38.degree. C.
Insufflation gases typically are delivered extremely dry. In accordance with Food and Drug Administration guidelines, medical grade carbon dioxide, the most prevalent gas used for laparoscopy, contains 200 parts per million or less of water vapor. The extreme lack of moisture in the insufflation gas can lead to drying of exposed tissue surface within the abdomen, and to the possibility of adhesion formation within the peritoneal cavity Corfman, R. C., Clinical Consultations in Obstetrics and Gynecology, 1:41-49 (1989)). With previous insufflation systems, frequent irrigation of the peritoneal cavity was required to limit adhesion formation.
The Douglas et al. patent discloses humidifying the insufflation gas prior to administration to the patient. Its method and device to achieve this objective, however, does not allow for a number of important thermodynamic and psychrometric effects. For instance, it is not effective to thermally condition and then to humidify the gas (or visa versa) in a serial order (see, for example, Chapter 5, Psychrometrics, ASHRAE Handbook, Fundamentals, Section I, (The American Society of Heating, Refrigerating and Air Conditioning Engineers, Inc., pp. 5.1-5.10 (1981)). Because of the,intrinsic nature of the dependency of water vapor pressure upon temperature, it is not possible to obtain useful levels of relative humidity and temperature with the Douglas et al. device.
It is known to filter insufflation gas to prevent inorganic particles such as metallic fillings or particles, rust, dust, and polymer particles from passing into the pneumoperitoneum (se, e.g., Ott, D. E., J. Gynecol. Surg., 5:205-208 (1989)). The location and type of filter, however, are very important factors which will influence the effectiveness of the method. Filters having a pore size as small as 0.2 microns have been used in previous insufflation systems. These devices, however, utilize a filter material that is typically hydrophilic and when it becomes moist, loses its strength and some of its filtering effectiveness. These filters, because they are not hydrophobic, can lose their filtering capability by tearing under the water pressure caused by accidentally suctioning peritoneal or irrigation fluids.
Typically, insufflators and other prior art insufflation gas conditioning methods utilize conventional, 120 volt, alternating current power commonly available in all operating rooms. There are two disadvantages to this power source: The number of devices requiring such power during surgery has become very large in recent years, which reduces space near the operating table and creates a tangle of power cords which compete for outlets and sometimes interfere with operating room procedures. Secondly, despite advanced grounding and isolation device and hospital procedures, there remains a finite probability of accidentally causing dangerous, sometimes lethal, patient shock from the 120 AC voltage.
Thus, previous devices attempting to provide conditioned gas to a patient have had significant problems and limitations. Accordingly, there is a great need for a method and apparatus for the conditioning of insufflation gas with appropriate physiological temperature, humidity and purity suitable for direct introduction to the peritoneal cavity in a manner which overcomes the limitations of previous systems.